The aim of this work is to assess the effect of loads statically or cyclically applied to the intact lumbar intervertebral motion segment in the mid-sagittal plane in vitro. The changes in the mechanical characteristics of the vertebral body-disc-vertebral body preparation will be measured. A combination of compression and flexion loads will be imparted to the preparations at a frequency of 9.5 cycles/sec. Changes in mechanical characteristics will be assessed before and after the cyclic or static load exposures via static load-deflection tests (in combined compression and flexion) and stereophotogrammetry (to assess three-dimensional vertebral body motion). The mechanical effect of a single overload event following the static or cyclic loading will be evaluated in a similar manner. Forty human cadaveric spine segments will be thus evaluated in a temperature and humidity controlled environment. The long term objective of this study is to correlate the mechanical changes due to a cyclic loading of the intervertebral motion segment to epidemiologic data showing an increased incidence of herniated nucleus pulposus in seated operators in vibration environments (i.e. long haul track drivers). Mechanical engineering techniques will be used to evaluate the preparations as if they were materials in a mechanical fatigue environment. The results of this study may help elucidate the mechanical factors involved in the production of low back pain in a vibration environment.